I can second this. I get routinely mistaken for a runner because of my size. I do strive for 10k steps a day, but generally, my activity levels would not easily reflect my BMI.

>People love to think of the body as a simple energy-in->energy-out equation, but it's definitely more complex than that, as the body can change what it's deciding to hold on to and what it's deciding to burn or expel.

If calories-in/calories-out didn't work, then it would be impossible to starve to death.

Where people get confused is that the number of calories changes as your metabolism speeds up or slows down.

If you are ingesting fewer calories than your body requires, you will lose some combination of fat and muscle. There is no possible way for this to be false.

It's the flip side that is quite possible to be false. You can certainly eat more calories than your body requires and yet not gain weight. Your gut could absorb less, so you excrete otherwise-digestible carbs. You could have a parasite.

Further, you could be burning more calories without doing more exercise or otherwise doing anything "useful" with the energy -- i.e. having a higher basal metabolic rate. These calories can be burned doing all sorts of things that the person has no control over: you could have a higher core body temperature, you could be spending more energy on cellular repair and other cellular processes, you could be synthesizing more hormones, you could be spending more energy metabolizing foods, etc etc.

These latter causes are obviously on the "energy out" side of the equation, but they do not relate to things under our control. Further, they can change with age, stress, and (relevant to TFA) sleep.

So a body that has been coasting by eating 2200 calories per day and never gaining a pound could suddenly change and start putting on weight, even though the person's diet and activities haven't changed.

The point is that two people could eat the exact same calories, and do the exact same exercise, and one of them go up in weight and the other go down. The "calories in vs calories out" idea usually simplistically makes people think this couldn't be true, because "calories out" is simplistically taken as "exercise."

The reason I shared my story is that so many people just quote "calories in vs calories out" as if both sides of the equation were perfectly under control, and those people are also often like me: they find it easy to keep the pounds off (because of a high metabolic rate) and so they look down on people who have trouble shedding weight and figure that those people could live just like them. But those heavier people could well be eating less and doing more exercise than them.

> It's the flip side that is quite possible to be false. You can certainly eat more calories than your body requires and yet not gain weight. Your gut could absorb less, so you excrete otherwise-digestible carbs. You could have a parasite.

Is the flip-side really debated that much tho? I feel like when people talk about CICO they're primarily talking about reducing CI to lower than your CO. No?

The complexity in CICO of course is measuring your CO. Ie you could estimate your CO, reduce your CI to what you believe your CO is - and still not lose weight. But does that undermine CICO? Because as the other commenters mentioned, it's "impossible" for you to burn more than you take in without losing mass, so our issue in this example is incorrectly asserting the output (assuming of course we're not also underestimating the input).

Note my questions here are generally questions. I am not an expert here, so please correct me if i'm wrong.

> The reason I shared my story is that so many people just quote "calories in vs calories out" as if both sides of the equation were perfectly under control, and those people are also often like me: they find it easy to keep the pounds off (because of a high metabolic rate) and so they look down on people who have trouble shedding weight and figure that those people could live just like them. But those heavier people could well be eating less and doing more exercise than them.

Fwiw, i don't dispute that some people have the wrong ideas with CICO. Perhaps frequently even. But i thought it still stood as a foundational truth nonetheless; that you have to "simply" burn more than you take in. If you gain weight (ignoring water weight for simplicity), then you have ate more then you burned, always.

My takeaway with CICO is that the hardest question seems to be correctly figuring out how much you're burning. Which i feel like usually, especially for overweight people, it's much less than they think. You can't outrun a bad diet, as they say. Rarely do people actually want to exercise enough to truly compensate for the thing they want to eat. Hence why i like CICO, as to me it signals the only effective action is in restricting your CI, since increasing CO is so difficult.

In my Indian family, this sort of skinny phenotype with a voracious appetite had a simple folk explanation - you eat so much that the food doesn't have time to be absorbed.

And yet, if you want to lose weight, it’s almost always (outside of medical conditions) as simple as getting into a caloric deficit that matches the deficit necessary to induce weight loss.

If you have a 500cal deficit per day, you lose a pound of weight (fat) per week. It’s literally that simple.

There’s some auto regulation of caloric burn rate, but it’s not some impossible problem to solve.

If you knew your exact metabolic requirements as well as the exact calorie count of every food you ingested, then it would be that simple. But what if you take the elevator one day instead of the stairs and don't burn off the 30 or so calories it might take to go up them? What if someone went a little heavy on the dressing on a salad you ordered and added 100 calories or so?

I've manipulated my body weight a few times and the real world is vastly different from a simple model of CI/CO.

On average this doesn’t matter. Humans are a whole lot more predictable and pattern based than you seem to be implying.

Also, if you’re trying to aim to a specific deficit, you should be calorie counting your food. If you got fatty dressing, you should be counting that. Even estimating is relatively easy once you do it for awhile. And if you don’t get it quite right, being a little off shouldn’t impact your overall average too much. It keeps you honest, which I think is by and large the main reason people don’t think they can lose weight: dishonest assessments of food consumption.

As I've said, I can absolutley lose weight, but I cannot reliably lose one pound per week; I do not seem to have that resolution in the numbers.

I've been tracking my weight weekly and all calories (even with crude estimates in some cases) for a year and a half, and have been experimenting with exactly this: I made a scatter plot and linear regression of average calories per day on the X axis, and weight change for that week on the Y axis.

Week to week weight has extra fluctuations that make it difficult to tell what's going on, but after around 6 months of data it stabilizes, and has been consistent for any 6-month period over the last year and a half: I burn around 2200 - 2300 calories per day on average (way higher than the online estimator tools think I burn, 1600 - 1700).

Knowing this I've also been reliably able to control my weight up or down at the rate I want as long as I'm looking at it for over a month span - because as above, week to week there's too much fluctuation (fullness of stomach and bowels mostly).

That it takes that much data to see the result pretty much proves my point - maintaining a 500 calorie per day deficit is just very difficult for me and I suspect most people. I don’t mean the hunger - when I do lose weight the deficits are easily above 1000, but 500 is too marginal for me to resolve.

Reliably losing one pound a week (beyond the initial 1-2 week period where your weight is going to go all over the place due to water weight fluctuations) is as simple as cutting calories until you see the weight (on average, ignore fluctuations) drop by 1 lb a week. You have to average extensively. Bodies are very temperamental at this, unfortunately. My scale weight swings 0.5-1 lb quite frequently mainly due to sodium changes in my diet. It’s all about trend weight, though.

I believe you confuse an inequality of Energy(Fat) ≤ Energy(Food) - Energy(Activity) with an equation and are trying to disprove it with a counter-example. People saying "calories in, calories out" don't help with this confusion too. Another variant of your argument is "but different people extract different amounts of energy from the same food so there!". This being an equality, both arguments make no sense. I give you more - the "Energy(Food)" is calculated by burning the food in question and measuring the energy produced. It's guaranteed to be more than most humans could extract from the food as most humans excrete more complex chemicals than carbon dioxide and water, which burning food produces. But it does not matter because this is an inequality and not an equation. E.g. in your example the inequality still holds, you allegedly increased the Energy(Food) but the energy stored in fat did not increase, as asserted in the inequality.

A counter example to disprove this would be somebody gaining more weight in fat than the weight of fat needed to store energy from consumed food. Of course, this would have been broken pretty fundamental laws of nature and would have caused some kind of revolution in physics.